Distributed Transaction Manager

Transcription

1 Distributed Transaction Manager

2 Pluggable transaction API CSP UDT FDW Core TM? AM

3 extensible Transaction API XidStatus (*GetTransactionStatus)(TransactionId xid, XLogRecPtr *lsn); void (*SetTransactionStatus)(TransactionId xid, int nsubxids, TransactionId *subxids, XidStatus status, XLogRecPtr lsn); Snapshot (*GetSnapshot)(Snapshot snapshot); TransactionId (*GetNewTransactionId)(bool issubxact); TransactionId (*GetOldestXmin)(Relation rel, bool ignorevacuum); bool (*IsInProgress)(TransactionId xid); TransactionId (*GetGlobalTransactionId)(void); bool (*IsInSnapshot)(TransactionId xid, Snapshot snapshot);

4 New commit callback events XACT_EVENT_START, XACT_EVENT_COMMIT, XACT_EVENT_PARALLEL_COMMIT, XACT_EVENT_ABORT, XACT_EVENT_PARALLEL_ABORT, XACT_EVENT_PREPARE, XACT_EVENT_PRE_COMMIT, XACT_EVENT_PARALLEL_PRE_COMMIT, XACT_EVENT_PRE_PREPARE, XACT_EVENT_COMMIT_PREPARED, XACT_EVENT_ABORT_PREPARED

5 Transaction Manager before patch transam/clog.c: GetTransactionStatus SetTransactionStatus transam/varsup.c: GetNewTransactionId ipc/procarray.c: TransactionIdIsInProgress GetOldestXmin GetSnapshotData time/tqual.c: XidInMVCCSnapshot

6 Transaction Manager after patch Transaction Manager transam/clog.c: GetTransactionStatus SetTransactionStatus transam/varsup.c: GetNewTransactionId ipc/procarray.c: TransactionIdIsInProgress GetOldestXmin GetSnapshotData time/tqual.c: XidInMVCCSnapshot

7 Distributed Transaction Manager Transaction Manager transam/clog.c: GetTransactionStatus SetTransactionStatus transam/varsup.c: GetNewTransactionId ipc/procarray.c: TransactionIdIsInProgress GetOldestXmin GetSnapshotData time/tqual.c: XidInMVCCSnapshot pg_dtm.so

8 Different DTM implementations Local transactions 2PC Arbiter Examples Snapshot sharing Timestamp Incremental XL, DTM Spanner, Cockroach, tsdtm SAP HANA

9 DTM architecture PostgreSQL Instance 1 Arbiter slave 1 asynchronous replication PostgreSQL Instance 2 Arbiter master synchronous replication PostgreSQL Instance 3 Arbiter slave 2

10 DTM from client's point of view Primary server Secondary server create extension pg_dtm; create extension pg_dtm; select dtm_begin_transaction(); begin transaction; update...; commit; select dtm_join_transaction(xid); begin transaction; update...; commit;

11 Arbiter protocol (begin) node a begin xid, snaphsot, gxmin join(xid) dtmd node b snaphsot, gxmin

12 Arbiter protocol (end) node a commit(xid) ok commit(xid) dtmd node b ok

13 DTM transaction control flow Assign XID Vote Arbiter dtm_begin_ transaction begin transaction commit transaction Node 1 XID dtm_join_ transaction begin transaction commit transaction Node 2 dtm_join_ transaction begin transaction commit transaction Node 3

14 tsdtm architecture PostgreSQL Instance 1 PostgreSQL Instance 2 PostgreSQL Instance 3

15 tsdtm transaction control flow prepare transaction commit prepared Node 1 snapshot prepare transaction Node 2 max CSN commit prepared prepare transaction commit prepared Node 3

16 Lightweight two-phase commit XactLogCommitRecord (flush changes in WAL) Transaction status TransactionTreeSetCommitTsData (set transaction status in CLOG) Arbiter ProcArrayEndTransaction (mark transaction as completed) ResourceOwnerRelease (release transaction locks)

17 Multiplexing backends Node 1 sockhub Unix domain sockets TCP sockets backends Node 2 Arbiter Unix domain sockets

18 Example of interaction with DTM xid := execquery(con1, "select dtm_begin_transaction()") exec(con2, "select dtm_join_transaction($1)", xid) exec(con1, "begin transaction") exec(con2, "begin transaction") exec(con1, "update t set v = v + $1 where u=$2", amount, account1) exec(con2, "update t set v = v - $1 where u=$2", amount, account2) var wg sync.waitgroup wg.add(2) asyncexec(con1, commit, &wg) asyncexec(cnn2, commit, &wg) wg.wait()

19 Example of interaction with tsdtm exec(con1, "begin transaction") exec(con2, "begin transaction") snapshot = execquery(con1, "select dtm_extend($1)", gtid) snapshot = execquery(con2, "select dtm_access($1, $2)", snapshot, gtid) exec(con1, "update t set v = v + $1 where u=$2", amount, account1) exec(con2, "update t set v = v - $1 where u=$2", amount, account2) exec(con1, "prepare transaction '" + gtid + "'") exec(con2, "prepare transaction '" + gtid + "'") exec(con1, "select dtm_begin_prepare($1)", gtid) exec(con2, "select dtm_begin_prepare($1)", gtid) csn = execquery(con1, "select dtm_prepare($1, 0)", gtid) csn = execquery(con2, "select dtm_prepare($1, $2)", gtid, csn) exec(con1, "select dtm_end_prepare($1, $2)", gtid, csn) exec(con2, "select dtm_end_prepare($1, $2)", gtid, csn) exec(con1, "commit prepared '" + gtid + "'") exec(con2, "commit prepared '" + gtid + "'")

20 Example of using FDW exec(con, "select dtm_begin_transaction()") exec(con, "begin transaction") exec(con, "update t set v = v + $1 where u=$2", amount, account1) exec(con, "update t set v = v - $1 where u=$2", amount, account2) exec(con, commit )

21 Example of using pg_shard exec(con, "begin transaction") exec(con, "update t set v = v + $1 where u=$2", amount, account1) exec(con, "update t set v = v - $1 where u=$2", amount, account2) exec(con, commit )

22 Test configuration Client 1 Client 2 Worker 1 Worker 2 Worker 1 Worker 1 Arbiter

23 Performance measurement ktps 100 Simple bank debit/credit benchmark (a-la TPC-A) Two clients with 60 writers pg_shard fdw w/o DTM with DTM Nodes

24 Multimaster performance Simple update/select queries Three clients with 140 readers ktps no writers 8 writers Nodes

25 Roadmap Add XTM patch to PostgreSQL 6 Experiment with different DTM implementations Provide integration of DTM with different cluster solutions (pg_shard, FDW, XL,...) Implement multimaster on top of DTM